File upload bugs out if more than one line is used in dialogue

[Slider-Whistle]

I'm not entirely sure this is what causes the bug, but the filename I was trying to use was
~/import/3ffd2e08ab2741ba9faeab1f1c6c4c894004c048.jpg. Absolute paths didn't work, either, so I think it's the length of the filename which causes the bug.
It might be worth nothing that the normal "File not found!" response doesn't appear if you enter an invalid filename of about the same length.